#!/usr/bin/env perl

use utf8;

$pi = 3.141592654;

$rad=undef;

$circum = undef;

$rad = <STDIN>;

if(defined($rad)){
	chomp($rad);
	$circum = 2 * $pi * $rad;
	print "The circum of rad $rad is $circum\n";
}
else{
	print "Please input a correct num\n";
}
